.TH std::codecvt::max_length,do_max_length 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::codecvt::max_length,do_max_length \- std::codecvt::max_length,do_max_length

.SH Synopsis
   Defined in header <locale>
   public:                                             \fI(until C++11)\fP
   int max_length() const throw();
   public:                                             \fI(since C++11)\fP
   int max_length() const noexcept;            \fB(1)\fP
   protected:                                                        \fI(until C++11)\fP
   virtual int do_max_length() const throw();      \fB(2)\fP
   protected:                                                        \fI(since C++11)\fP
   virtual int do_max_length() const noexcept;

   1) Public member function, calls the member function do_max_length of the most
   derived class.
   2) Returns the maximum value that do_length(state, from, from_end, 1) can return for
   any valid range [from, from_end) and any valid state.

.SH Return value

   The maximum number of ExternT characters that could be consumed if converted by in()
   to produce one InternT character.

   The non-converting specialization std::codecvt<char, char, std::mbstate_t> returns
   1.

.SH Notes

   If the encoding is state-dependent (encoding() == -1), then more than max_length()
   external characters may be consumed to produce one internal character.

.SH Example


// Run this code

 #include <codecvt>
 #include <iostream>
 #include <locale>

 int main()
 {
     std::cout << "In codecvt_utf8, the longest multibyte character is "
               << std::codecvt_utf8<wchar_t>().max_length() << " bytes long\\n";

     std::cout << "In header-consuming codecvt_utf8, the longest multibyte character is "
               << std::codecvt_utf8<wchar_t,
                                    0x10ffff,
                                    std::consume_header>().max_length() << " bytes long\\n";

     std::cout << "In this system's en_US.utf8, the longest multibyte character is "
               << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                      std::locale("en_US.utf8")
                  ).max_length() << " bytes long\\n";

     std::cout << "In this system's zh_CN.gb18030, the longest multibyte character is "
               << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                      std::locale("zh_CN.gb18030")
                  ).max_length() << " bytes long\\n";
 }

.SH Output:

 In codecvt_utf8, the longest multibyte character is 4 bytes long
 In header-consuming codecvt_utf8, the longest multibyte character is 7 bytes long
 In this system's en_US.utf8, the longest multibyte character is 6 bytes long
 In this system's zh_CN.gb18030, the longest multibyte character is 4 bytes long

.SH See also

   MB_CUR_MAX  maximum number of bytes in a multibyte character in the current C locale
               (macro variable)
   do_encoding returns the number of ExternT characters necessary to produce one
   \fB[virtual]\fP   InternT character, if constant
               \fI(virtual protected member function)\fP
